Electric hub motor improves EV range: Part 1—Technology basics

The following computations are done with a 0.6-T field, in order to be conservative or allow the use of cheaper magnets.

Printed circuit disks are made of two networks, each made of 24 radial wires (shown in red and green in the previous figures), connected as “serpentines.” The series resistance of the wires is assumed to be the resistance of the radial axes, as the circular connections can be designed sufficiently thick for essentially zero resistance. The cross section of the radial wires is 2 mm2 (4 mm large x 0.5-mm thick) in the center part of the disk, up to 8 mm2 (16 mm x 0.5 mm) in the outer part.

The twin networks are powered with 90° phase difference, as shown below, in order to maintain the motor torque during the switching time of the current on the complementary phase.

The length of the 24 wires is 24 * 15 cm = 3.6m. The rotation force on these wires is:

F = B * I * l = 0.6 * 3.6 * I = 2.16 * I

This force is applied in the middle of the wires, at a distance from the axis of 12.5 cm. The motor torque per stack is

Γ = F * r = 2.16 * 0.125 * I = 0.27 * I

The total motor torque generated by the 12 stacks is:

Γtot = 12 * 0.27 * I = 3.24 * I

A 30A current generates a mechanical torque of 97.2 Nm.

A vehicle driven by four wheels has a total driving torque of 390 Nm, when 30A is flowing through all stacks. This corresponds to the driving torque of existing high-performance cars.

A 15-cm copper wire, with a cross section varying between 2 mm2 and 8 mm2 has a resistance of 6 µΩ. Assuming that interconnections between radial wires have a negligible resistance, the total resistance of a printed circuit disk wire is 24 * 6 = 0.145 mΩ.

A 30A current flowing through this wire generates a 4.5 mV voltage drop, and 130 mW power dissipation. The total power dissipation for the 12 stacks of a wheel, when 30A are flowing in all disks is 1.6W.

All wires of all stacks are connected to the command circuitry, located close to the axle. Each wire is connected to an electronic switch, with a series resistance of 0.2 Ω (conservative number, in order to take into account unexpected parasitic resistances). This switch represents the major contribution in the estimated total resistance of the electric circuit, and generates most of the joule losses (carefull selection of these MOS transistors has a direct impact on the energetic yield of the system).

The switches need to be able to handle both high current in one scenario and high voltage in the other extreem.
So the semiconductors size and cost go throught the roof, add the IR loss gain for needed worst case voltage needed, making this not feasible quickly.

Has anyone heard of BionX, www.bionx.ca? They make hub motors used in boost systems for bicycles and velomobiles. Their systems go up to 500 watts and are priced around $2,000 with a control system using regenerative braking, http://www.youtube.com/watch?v=eSFE151tRdM. Is the system described here better or cheaper than the BionX system?
I want to mass produce velomobiles with boost systems controlled by I-pads, and could use the help of some smart guys like you.

Readers are directed to two sites:
http://www.technologyreview.com/energy/21666/
http://www.launchpnt.com/portfolio/aerospace/uav-electric-propulsion/
It doesn't look like Exro weathered the recession very well since I haven't seen anything from them lately, but my original analysis of their approach/patent (switched coils to change torque characteristics) led me to believe that the engineering was sound. Likewise for LaunchPoint.

I think you are getting confused between cm and mm. A 10cm(100mm) axil will, depending on what it is made from will easily hand up to 5 x 1.5 tons. I've lifted components up to 30 tons on pins that thick.

Thats kinda scarey, just anyone that knows enough to be dangerous can post all this with the editor of EE times to go ahead and let it happen. I guess thats the downside of this kind of forum. The good side is that someone like roldan speaks up to reprove it, but is he right?

Two years ago "EE Times" reported that "Daimler bus combines hub motors, fuel cells" (http://www.eetimes.com/electronics-news/4197774/Daimler-bus-combines-hub-motors-fuel-cells) so it would appear that the deployment problems for hub motors are not insurmountable. It sounds like one challenge will relate to car handling characteristics having additional mass that will be moving with the wheels (rather than the vehicle body). This is probably less of an issue for a bus. Another design issue will be to ensure that the hub mounted motors are designed to tolerate exposure to the elements near the wheels rather than being protected in the engine compartment.

I would very much like to be a naive high school kid. Unfortunately, I am a retired electronics engineer, with 40 years of background in the industry, acting now as an independent consultant. Almost twenty patents filed. Six presentations at international conferences. One invited paper at ISSCC. My career is behind me.
To be fully honnest, when I tried to patent this concept, I found that this was already done almost twenty years ago. There are at least two naive high school kids dreaming in the world. But, apparently, the other one failed in promoting the concept.
I think, but you can disagree, that it can be very beneficial for the whole industry, and not only the automotive one. For an independent consultant, the automotive industry is too big. I'm more interested in other applications, looking for attractive small niches. But, if I can convince the automotive industry to go in this direction, this should help for developing smaller businesses.
I would enjoy replying to technical questions. In your comment, I can't see any requesting an answer. Please, consider the concept, and not the implementation details.